Several reasons (for example financial or regulatory) nowadays force mobile radio operators to efficiently utilize, jointly operate or share parts of the infrastructure for providing mobile radio services. In this respect, national roaming agreements are known, where the mobile radio subscribers of one mobile radio operator are permitted to use the mobile access network and also the core network of the respective roaming partner.
A method for several mobile network operators to jointly use a radio access network is described in international patent application WO 2005/013583 A2. This method requires that the mobile device selects the PLMN (Public Land Mobile Network) in a way different to the PLMN selection implemented in many (older) mobile devices (hereinafter also called mobile terminals) according to the GSM/GERAN standard which means that older GERAN mobile terminals cannot be used or only used according to a restricted mode of operation. Especially, the method according to international patent application WO 2005/013583 A2 requires a mobile device to actively transmit the PLMN identifier (Public Land Mobile Network identifier) information of the chosen mobile network operator to the base station whereas older GERAN mobile terminals conduct the PLMN selection according to a frequency selection (of a radio frequency channel).
At present, GERAN (GSM EDGE Radio Access Network) mobile radio access networks are the dominant standard for mobile radio networks. However, mobile radio networks are progressively modernized in order to comply with next generation mobile radio network standards such as NGMN (Next Generation Mobile Network) or LTE (Long Term Evolution)/E-UTRAN (Evolved Universial Terrestrial Radio Access Network). Even in the case a mobile radio network operator has successfully migrated its clients from GERAN networks to networks of the next generation, the need will persist to provide mobile radio network services according to the GERAN standard.